[CMOTD]

Assuming you mean the two bits that look like a Biro tube inner which slip over the axle and prevent it sliding about:
Measurements taken from my C25 Ferrari 312B2 - external diameter 4.6mm, internal diameter 2.3mm, length 12.1mm. Wouldn't guarantee that they are the same on other F1 cars of the era though, a lot of component variety back then.

Modern Biro tube inners are too small if you were thinking of using them as replacements.